Liquid crystal display device and method of manufacturing a liquid crystal display device

ABSTRACT

A liquid crystal display device ( 10 ) includes: gate wiring ( 501 ) formed on a substrate ( 500 ) and along a first direction; drain wiring ( 702 ) formed on the substrate ( 500 ) and along a second direction that is different from the first direction; a common electrode ( 900 ) formed so as to cover the drain wiring ( 702 ) through intermediation of an insulating film ( 800 ); and common wiring ( 901 ) formed on the common electrode ( 900 ) and along the drain wiring ( 702 ). The common wiring ( 901 ) is formed so that at least a part of the common wiring ( 901 ) overlaps with a region in which the drain wiring ( 702 ) is formed.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese application JP2012-162953 filed on Jul. 23, 2012, the content of which is herebyincorporated by reference into this application.

TECHNICAL FIELD

The present application relates to a liquid crystal display device and amethod of manufacturing a liquid crystal display device.

BACKGROUND

A liquid crystal display device includes a thin film transistorsubstrate (TFT substrate) for displaying an image on a display surfaceby controlling transmission/non-transmission of light from a backlightunit through a liquid crystal material provided between the backlightunit and the display surface. The thin film transistor substrateincludes a transparent substrate, a gate electrode arranged on thetransparent substrate, a gate insulating film arranged on the gateelectrode, a semiconductor layer arranged on the gate insulating film, asource electrode and a drain electrode arranged on the semiconductorlayer, a protective insulating film arranged on the source electrode andthe drain electrode, and a pixel electrode connected to the sourceelectrode or the drain electrode. A part of the semiconductor layer,which is formed between the source electrode and the drain electrode,corresponds to a channel forming region in which a channel is to beformed.

FIG. 14 is a conceptual diagram of a pixel circuit 1401 formed of a thinfilm transistor 1402. The pixel circuit 1401 provided in the thin filmtransistor substrate controls transmission/non-transmission of lightfrom the backlight unit provided so as to be opposed to the thin filmtransistor substrate.

One of a source and a drain of the thin film transistor 1402 isconnected to a video signal line 1403, and the other of the source andthe drain is connected to a pixel electrode 1404. In an in-planeswitching (IPS) mode liquid crystal display device, the pixel electrode1404 and a common electrode 1405 are formed in the thin film transistorsubstrate.

A video signal and a reference potential are applied to the video signalline 1403 and the common electrode 1405, respectively. Further, ON/OFFof the thin film transistor 1402 is controlled by a gate signal, tothereby change a potential difference between the pixel electrode 1404and the common electrode 1405. A liquid crystal material 1406 sealedbetween the thin film transistor substrate and a color filter changesits orientation in accordance with the change of the potentialdifference (generated in a direction parallel to the surface of the thinfilm transistor substrate), and thus the transmission/non-transmissionof light from the backlight unit is controlled.

Japanese Patent Application Laid-open No. 2009-122299 discloses a liquidcrystal display device in which a counter voltage signal line forsupplying a reference signal to a counter electrode is formed along arunning direction of a gate signal line so as to overlap with the gatesignal line, to thereby improve the aperture ratio.

SUMMARY

Hitherto, the liquid crystal display device has been used forapplications that require a laterally-long display surface, such as apersonal computer (PC) and a television set, but along with thepopularization in recent years of an information processing device(tablet PC) and multifunctional cellular phone (smart phone) having avertically-long planar shape, there is a growing demand for a liquidcrystal display device having a vertically-long display surface.Further, there are cases where the thin film transistor, a base for aspacer, or the like is provided on the gate signal line. When thecounter voltage signal line is formed along the running direction of thegate signal line so as to overlap with the gate signal line, it isnecessary to wire the counter voltage signal line while avoiding thethin film transistor and the like, or wire the counter voltage signalline in a space obtained by expanding the gate signal line. In theformer case, the wiring becomes complicated and a risk of disconnectionincreases, while in the latter case, the aperture ratio may reduce insome cases.

It is an object of the present implementation to provide a liquidcrystal display device and a method of manufacturing a liquid crystaldisplay device that are suitable for applications requiring avertically-long display surface. Further, it is another object of thepresent implementation to provide a liquid crystal display device and amethod of manufacturing a liquid crystal display device that are capableof preventing reduction in aperture ratio with a relatively-simplewiring design.

In order to solve the above-mentioned problem, a liquid crystal displaydevice according to one embodiment of the present application includes:gate wiring formed on a substrate and along a first direction; drainwiring formed on the substrate and along a second direction that isdifferent from the first direction; a common electrode formed so as tocover the drain wiring through intermediation of a first insulatingfilm; and common wiring formed on the common electrode and along thedrain wiring. The common wiring is formed so that at least a part of thecommon wiring overlaps with a region in which the drain wiring isformed.

According to the one embodiment of the present application, the liquidcrystal display device is provided, in which the common wiring is formedalong the drain wiring so that at least a part of the common wiringoverlaps with the region in which the drain wiring is formed. When theliquid crystal display device is mounted on an information processingterminal or the like, generally, the drain wiring is formed in thevertical direction of the equipment. Further, potential fluctuationsthat occur due to the low conductivity of a tin-doped indium oxide (ITO)or the like, which is the material of the common electrode, notablyoccur particularly in the vertical direction in the vertically-longliquid crystal display device. In the present application, the commonwiring for supplying a potential to the common electrode is formed alongthe drain wiring, that is, in the vertical direction. Therefore, thepotential fluctuations are reduced, and as a result, more satisfactorydisplay characteristics may be obtained. Therefore, the liquid crystaldisplay device of the present application may be suitable used forapplications requiring a vertically-long display surface. Further, thecommon wiring is formed in the vertical direction, and thus a drivercircuit for the common wiring may be provided in a region above or belowthe thin film transistor substrate. Also in view of this point, theliquid crystal display device of the present application may be suitablyused for applications requiring a vertically-long display surface.Further, at least a part of the common wiring overlaps with the regionin which the drain wiring is formed. Therefore, a region in which lightis blocked by each wiring is reduced, and hence reduction in apertureratio can be prevented.

Further, in the one embodiment of the present application, the liquidcrystal display device further includes: a second insulating film formedso as to cover the common electrode and the common wiring; and a pixelelectrode formed on the second insulating film, at least a part of thepixel electrode overlapping with the common electrode.

Further, in the one embodiment of the present application, the commonwiring has opposing pattern edges that are each separated from a patternedge of the drain wiring at an interval of a predetermined width or morein plan view.

Further, in the one embodiment of the present application, thepredetermined width is determined to be larger than an interval in planview between the pattern edge of the drain wiring, and a boundarybetween, in a surface of the common electrode, a region that is inclineddue to the drain wiring and a region parallel to a surface of thesubstrate.

Further, in the one embodiment of the present application, thepredetermined width is 1 micrometer or more.

Further, in the one embodiment of the present application, one ofopposing pattern edges of the common wiring is formed on a surface ofthe common electrode in a region parallel to a surface of the substrateand above the region in which the drain wiring is formed.

Further, in the one embodiment of the present application, both ofopposing pattern edges of the common wiring is formed on a surface ofthe common electrode in a region parallel to a surface of the substrateand above the region in which the drain wiring is formed.

Further, in the one embodiment of the present application, both ofopposing pattern edges of the common wiring is formed on a surface ofthe common electrode in a region parallel to a surface of the substrateand outside the region in which the drain wiring is formed.

Further, in the one embodiment of the present application, one ofopposing pattern edges of the common wiring is formed in a regionparallel to a surface of the substrate and above the region in which thedrain wiring is formed, and another of the opposing pattern edges of thecommon wiring is formed in the region parallel to the surface of thesubstrate and outside the region in which the drain wiring is formed.

Further, a method of manufacturing a liquid crystal display deviceaccording to one embodiment of the present application includes: forminggate wiring on a substrate and along a first direction; forming drainwiring on the substrate and along a second direction that is differentfrom the first direction; forming a common electrode so as to cover thedrain wiring through intermediation of a first insulating film; andforming common wiring on the common electrode and along the drainwiring. The forming of the common wiring includes forming the commonwiring so that at least apart of the common wiring overlaps with aregion in which the drain wiring is formed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a view illustrating an example of a liquid crystal displaydevice according to an embodiment of the present application;

FIG. 2 is a view illustrating a configuration of a thin film transistorsubstrate provided in the liquid crystal display device according to theembodiment of the present application;

FIG. 3 is a view illustrating a structure of a cross-section taken alongthe line B-B in the thin film transistor substrate of FIG. 2;

FIGS. 4A and 4B are views illustrating examples of a cross-section ofthe thin film transistor substrate;

FIGS. 5A and 5B are views illustrating a method of manufacturing a thinfilm transistor substrate according to the embodiment of the presentapplication;

FIGS. 6A and 6B are views illustrating the method of manufacturing athin film transistor substrate according to the embodiment of thepresent application;

FIGS. 7A and 7B are views illustrating the method of manufacturing athin film transistor substrate according to the embodiment of thepresent application;

FIGS. 8A and 8B are views illustrating the method of manufacturing athin film transistor substrate according to the embodiment of thepresent application;

FIGS. 9A and 9B are views illustrating the method of manufacturing athin film transistor substrate according to the embodiment of thepresent application;

FIGS. 10A and 10B are views illustrating the method of manufacturing athin film transistor substrate according to the embodiment of thepresent application;

FIGS. 11A and 11B are views illustrating the method of manufacturing athin film transistor substrate according to the embodiment of thepresent application;

FIG. 12 is a view illustrating a configuration of a thin film transistorsubstrate according to another embodiment of the present application;

FIG. 13 is a view illustrating a configuration of a thin film transistorsubstrate according to further another embodiment of the presentapplication; and

FIG. 14 is a conceptual diagram of a pixel circuit formed of a thin filmtransistor.

DETAILED DESCRIPTION

FIG. 1 is a view illustrating an example of a liquid crystal displaydevice 10 according to an embodiment of the present application. Theliquid crystal display device 10 has a vertically-long display unit, andincludes a thin film transistor substrate 100 provided inside, forcontrolling image display on the display unit.

FIG. 2 is a view illustrating a configuration of the thin filmtransistor substrate 100 provided in the liquid crystal display device10 according to this embodiment. FIG. 3 is a view illustrating astructure of a cross-section taken along the line B-B in the thin filmtransistor substrate 100 of FIG. 2.

In the thin film transistor substrate 100, gate wiring 501 made of ametal such as Cu is formed on a substrate (transparent substrate) 500made of non-alkali glass or the like and along a lateral direction(first direction) of FIG. 1. Further, on the substrate 500 and the gatewiring 501, an insulating film (gate insulating film) 600 made of atransparent insulating material such as SiN is formed. On the insulatingfilm 600, drain wiring 702 made of a metal such as Cu is formed. Thedrain wiring 702 is formed along a vertical direction (second direction)of FIG. 1, which is different from the first direction. On theinsulating film 600 and the drain wiring 702, an insulating film(passivation film, first insulating film) 800 made of a transparentinsulating material such as SiN is formed.

A common electrode 900 formed of a transparent conductive film made of atin-doped indium oxide (ITO) or the like is formed so as to cover thedrain wiring 702 through intermediation of the insulating film 800.Common wiring 901 made of a metal such as Cu is formed on the commonelectrode 900 and along the drain wiring 702. In this case, the commonwiring 901 is formed so as to overlap with a region in which the drainwiring 702 is formed. Further, on the common electrode 900 and thecommon wiring 901, an insulating film (passivation film) 1000 is formed.On the insulating film 1000, a pixel electrode 1102 formed of atransparent conductive film made of a tin-doped indium oxide (ITO) orthe like is formed. A liquid crystal material 200 is sealed between acolor filter 300 and the insulating film 1000 and pixel electrode 1102.

Now, a region in which the common wiring 901 is formed is describedbelow. FIGS. 4A and 4B are views illustrating examples of across-section of the thin film transistor substrate. FIG. 4A illustratesa cross-section of the thin film transistor substrate 100 according tothis embodiment, and FIG. 4B illustrates a cross-section of the thinfilm transistor substrate in another form. In a form illustrated in FIG.4B, a width W_(c) of the common wiring 901 and a width W_(d) of thedrain wiring 702 are substantially equal to each other, and a patternedge of the common wiring 901 (a leading end part of the sectional shapeof the common wiring 901, which has an angle of θ_(b)) and a patternedge of the drain wiring 702 (a leading end part of the sectional shapeof the drain wiring 702, which has an angle of θ_(a)) substantiallyoverlap with each other in plan view (viewpoint from the upper side tothe lower side in FIGS. 4A and 4B).

In each of the surfaces of the insulating film 800 and the commonelectrode 900, due to the step formed by the pattern edge of the drainwiring 702, an inclined surface is formed at an angle of θ_(a) that isequal to that of the pattern edge. In the thin film transistor substrateillustrated in FIG. 4B, the pattern edge of the common wiring 901 andthe pattern edge of the drain wiring 702 substantially overlap with eachother in plan view. Therefore, when the common wiring 901 is formed, dueto the angle θ_(b) of the pattern edge of the common wiring 901, a taperangle of θ_(a)+θ_(b) is formed with respect to the substrate surface(horizontal surface) in the vicinity of the pattern edge of the commonwiring 901. When this angle has a relatively large value that exceeds90°, for example, in rubbing processing of rubbing the surface of thethin film transistor substrate 100 in one direction with cloth to alignthe directions of liquid crystal molecules, which is carried out in thesubsequent step, the cloth may not reach the (inner) surface that formsthe taper angle. Thus, the rubbing processing may not be sufficientlycarried out, and therefore satisfactory orientation may not be obtained.

In contrast, in the thin film transistor substrate 100 according to thisembodiment illustrated in FIG. 4A, the width W_(c) of the common wiring901 is smaller than the width W_(d) of the drain wiring 702, and thepattern edge of the common wiring 901 and the pattern edge of the drainwiring 702 do not overlapping with each other in plan view. As a result,when the common wiring 901 is formed, the taper angle formed withrespect to the substrate surface (horizontal surface) in the vicinity ofthe pattern edge of the common wiring 901 is suppressed to θ_(b) formedby the pattern edge of the common wiring 901. With this, even in therubbing processing, the cloth reaches the surface that forms the taperangle, and the rubbing processing is sufficiently carried out.

In this case, the width W_(c) of the common wiring 901 is defined sothat the pattern edge of the common wiring 901 is separated from thepattern edge of the drain wiring 702 at an interval of a predeterminedwidth w or more in plan view. The predetermined width w is determinedbased on the sectional shape of the pattern edge of the drain wiring702. For example, the predetermined width w is determined based on thedimensions of a region in the surface of the common electrode 900, whichis inclined due to the pattern edge of the drain wiring 702. Forexample, the predetermined width w is determined to be larger than aninterval in plan view between the pattern edge of the drain wiring 702,and a boundary between, in the surface of the common electrode 900, theregion inclined due to the drain wiring 702 and a region parallel to thesurface of the substrate 500. The predetermined width w is defined tobe, for example, 1 micrometer or more.

With the configuration described above, the liquid crystal displaydevice 10 including the thin film transistor substrate 100 is provided,in which the common wiring 901 is formed along the drain wiring 702 sothat at least a part of the common wiring 901 overlaps with the regionin which the drain wiring 702 is formed (in FIG. 2, a region defined bybroken lines representing the drain wiring 702). In this case, thecommon wiring 901 is formed along the drain wiring 702 formed along thevertical direction of the liquid crystal display device 10 (verticaldirection in FIG. 2), that is, the common wiring 901 is formed along thevertical direction. Therefore, in the thin film transistor substrate100, potential fluctuations are reduced, which notably occur in thevertical direction due to the low conductivity of ITO that is thematerial of the common electrode 900. Thus, more satisfactory displaycharacteristics can be obtained. Therefore, the thin film transistorsubstrate 100 may be suitably applied to the liquid crystal displaydevice 10 having a vertically-long shape. Further, the common wiring 901is formed in the vertical direction, and thus a driver circuit for thecommon wiring 901 can be provided in a region above or below the thinfilm transistor substrate 100. Also in view of this point, the thin filmtransistor substrate 100 may be suitably applied to the liquid crystaldisplay device 10 having a vertically-long shape. Further, at least apart of the common wiring 901 overlaps with a region in which the drainwiring 702 is formed, and thus a region in which light is blocked byeach wiring is reduced. Therefore, the reduction in aperture ratio canbe prevented as well.

Next, a method of manufacturing the thin film transistor substrate 100of the liquid crystal display device 10 according to this embodiment isdescribed. FIGS. 5A to FIG. 11B are views illustrating the method ofmanufacturing the thin film transistor substrate 100 according to thisembodiment. In FIGS. 5A to FIG. 11B, FIGS. 5A, 6A, 7A, 8A, 9A, 10A, and11A illustrate a structure of a cross-section taken along the line A-Aof FIG. 2, and FIGS. 5B, 6B, 7B, 8B, 9B, 10B, and 11B illustrate astructure of a cross-section taken along the line B-B of FIG. 2.

First, as illustrated in FIGS. 5A and 5B, on the substrate 500, the gatewiring 501 is formed along the lateral direction (first direction) ofFIG. 1. The gate wiring 501 is formed as follows. A Cu film is formed onthe substrate 500 by sputtering, and then unnecessary parts of the Cufilm are removed by a photolithography process (application of aphotoresist, selective exposure with use of a photomask, anddevelopment) and etching.

Next, as illustrated in FIGS. 6A and 6B, on the substrate 500, theinsulating film 600 is formed by, for example, CVD so as to cover thegate wiring 501. Further, on the insulating film 600, a semiconductorlayer 601 made of amorphous silicon (aSi) is formed. The semiconductorlayer 601 is processed into a predetermined shape by a photolithographyprocess and etching.

Next, as illustrated in FIGS. 7A and 7B, a drain electrode 700 and asource electrode 701 are formed on the semiconductor layer 601 and thedrain wiring 702 is formed on the insulating film 600 by aphotolithography process and etching. In this case, the drain wiring 702is formed along the vertical direction (second direction) of FIG. 1,which is different from the first direction.

Next, as illustrated in FIGS. 8A and 8B, the insulating film 800 isformed by, for example, CVD. Further, the insulating film 800 isprocessed by photolithography to form a contact hole 801. Then, asillustrated in FIGS. 9A and 9B, the common electrode 900 is formed bysputtering, and further, the common wiring 901 is formed by aphotolithography process and etching. In this case, the common electrode900 is formed so as to cover the drain wiring 702 through intermediationof the insulating film 800, and the common wiring 901 is formed alongthe drain wiring 702. Further, at least a part of the common wiring 901is formed so as to overlap with the region in which the drain wiring 702is formed.

Further, as illustrated in FIGS. 10A and 10B, the insulating film 1000is formed by, for example, CVD, and the insulating film 1000 isprocessed by a photolithography process and etching to form a contacthole 1001.

Next, a metal film is formed on the insulating film 1000, and the metalfilm is processed by a photolithography process and etching, to therebyform the pixel electrode 1102 as illustrated in FIGS. 11A and 11B.

With the above-mentioned steps, the thin film transistor substrate 100according to this embodiment is manufactured.

Note that, in the above-mentioned embodiment, description is made of aconfiguration in which the width W_(c) of the common wiring 901 issmaller than the width W_(d) of the drain wiring 702, and both of theopposing pattern edges of the common wiring 901 are formed on thesurface of the common electrode 900 in a region parallel to the surfaceof the substrate 500 and above the region in which the drain wiring 702is formed. However, the present application is not limited thereto, andother configurations may be adopted as long as the configuration doesnot cause increase in taper angle in the pattern edge of the commonwiring 901 due to the pattern edge of the drain wiring 702.

FIGS. 12 and 13 are views illustrating configurations of the thin filmtransistor substrate 100 according to other embodiments of the presentapplication. In FIG. 12, both of the opposing pattern edges of thecommon wiring 901 are formed on the surface of the common electrode 900in regions parallel to the surface of the substrate 500 and outside theregion in which the drain wiring 702 is formed. In FIG. 13, one of theopposing pattern edges of the common wiring 901 is formed in a regionparallel to the surface of the substrate 500 and above the region inwhich the drain wiring 702 is formed. Also in those configurations, thepattern edge of the common wiring 901 and the pattern edge of the drainwiring 702 are separated from each other at an interval of apredetermined width or more, similarly to the above-mentionedembodiment. Further, in the case where the pattern edge of the commonwiring 901 is formed outside the region in which the drain wiring 702 isformed, even when the pattern edge of the common wiring 901 is separatedat the interval of a predetermined width or more of the above-mentionedembodiment, when the inclined surface (side surface) of the commonwiring 901 overlaps with the inclined surface in the surface of thecommon electrode 900, the inclined surface of the common wiring 901 maybecome steep. Therefore, in such a case, the common wiring 901 may beformed so as to be separated from the pattern edge of the drain wiring702 at a larger interval to the extent that the inclined surface of thecommon wiring 901 does not overlap with the inclined surface in thesurface of the common electrode 900. Also with those configurations,effects similar to those in the above-mentioned embodiment are obtained.

In the above, the specific embodiments of the present application havebeen described, but the present application is not limited to theabove-mentioned embodiments, and various modifications may be made asappropriate without departing from the spirit of the presentapplication.

1-10. (canceled)
 11. A liquid crystal display device, comprising: a gatewiring disposed on a substrate and along a first direction; a firstwiring disposed on the substrate and along a second direction that isdifferent from the first direction; a second wiring disposed along thesecond direction, at least a part of the second wiring overlapping withthe first wiring in plan view; a first insulating film disposed betweenthe first wiring and the second wiring; and a common electrode disposedover the first insulating film, wherein one of the first wiring and thesecond wiring is electrically connected with the common electrode,wherein the first insulating film has a raised portion disposedoverlapping the first wiring in plan view, wherein one of opposingpattern edges of the second wiring overlaps with the raised portion ofthe first insulating film in plan view, and an other of the opposingpattern edges of the second wiring is disposed overlapping a regionlocated outside the region in which the raised portion of the firstinsulating film is disposed in plan view.
 12. The liquid crystal displaydevice of claim 11, wherein the first wiring is a common line and thesecond wiring is a drain line.
 13. The liquid crystal display device ofclaim 11, wherein the first wiring is positioned closer to the substratethan the second wiring.
 14. The liquid crystal display device of claim11, wherein both of the opposing pattern edges of the first wiring havean angle of less than 90 degrees with respect to a bottom surface of thecommon wiring.
 15. The liquid crystal display device of claim 11,wherein the common wiring has a portion which is wider than the drainwiring in a cross sectional view along the first direction.
 16. Theliquid crystal display device of claim 11 further comprising a pixelelectrode, wherein the common electrode is positioned far from thesubstrate than the pixel electrode.